Ok, This is realy odd. i just got a AR today (YAY!)
and i get on his website for codes. http://us.codejunkies.com/search/codes/cheat_codes.aspx?selp=3&game=Pokemon-Diamond&gameID=17826135&page=1
and did walk, and run through walls. (you must do both at the same time as far as i know.)
so, i was curious, and i went to pokemon leauge, go past that,to mirror rock, and there is a glitch, there is shayman. i go a little farther up and it dissapears. so down seabreak path, and then endup at the flower patch thing. then i see shayman. isn't that Wierd. and you can catch it too.if you have this glitch, or another like it on a nintendo event, reply!